Problem: Graph this system of equations and solve. $12x+8y = 40$ $-x+4y = -8$ $1$ $2$ $3$ $4$ $5$ $6$ $7$ $8$ $9$ $10$ $\llap{-}2$ $\llap{-}3$ $\llap{-}4$ $\llap{-}5$ $\llap{-}6$ $\llap{-}7$ $\llap{-}8$ $\llap{-}9$ $\llap{-}10$ $1$ $2$ $3$ $4$ $5$ $6$ $7$ $8$ $9$ $10$ $\llap{-}2$ $\llap{-}3$ $\llap{-}4$ $\llap{-}5$ $\llap{-}6$ $\llap{-}7$ $\llap{-}8$ $\llap{-}9$ $\llap{-}10$ Click and drag the points to move the lines.
Convert the first equation, $12x+8y = 40$ , to slope-intercept form. $y = -\dfrac{3}{2} x + 5$ The y-intercept for the first equation is $5$ , so the first line must pass through the point $(0, 5)$ The slope for the first equation is $-\dfrac{3}{2}$ . Remember that the slope tells you rise over run. So in this case for every $3$ positions you move down (because it's negative) You must also move $2$ positions to the right. $2$ positions to the right. $3$ positions down from $(0, 5)$ is $(2, 2)$ Graph the blue line so it passes through $(0, 5)$ and $(2, 2)$ Convert the second equation, $-x+4y = -8$ , to slope-intercept form. $y = \dfrac{1}{4} x - 2$ The y-intercept for the second equation is $-2$ , so the second line must pass through the point $(0, -2)$ The slope for the second equation is $\dfrac{1}{4}$ . Remember that the slope tells you rise over run. So in this case for every $1$ position you move up You must also move $4$ positions to the right. $4$ positions to the right. Graph the green line so it passes through $(0, -2)$ and $(4, -1)$ The solution is the point where the two lines intersect. The lines intersect at $(4, -1)$.